The Gran Sasso muon puzzle

TL;DR

This study analyzes over 20 years of muon flux data from Gran Sasso to investigate potential correlations with DAMA's annual modulation and solar cycle, finding incompatible phases and a surprising 11-year cycle in muon data.

Contribution

It provides the first detailed time-series analysis of combined muon flux data at Gran Sasso, revealing unexpected long-term periodicities and phase discrepancies with DAMA's modulation.

Findings

Muon flux shows a 1-year cycle with phase incompatible with DAMA.

Detected an 11-year cycle in muon data aligned with the solar cycle.

No long-term oscillation observed in stratospheric temperature data.

Abstract

We carry out a time-series analysis of the combined data from three experiments measuring the cosmic muon flux at the Gran Sasso laboratory, at a depth of 3800 m.w.e. These data, taken by the MACRO, LVD and Borexino experiments, span a period of over 20 years, and correspond to muons with a threshold energy, at sea level, of around 1.3 TeV. We compare the best-fit period and phase of the full muon data set with the combined DAMA/NaI and DAMA/LIBRA data, which spans the same time period, as a test of the hypothesis that the cosmic ray muon flux is responsible for the annual modulation detected by DAMA. We find in the muon data a large-amplitude fluctuation with a period of around one year, and a phase that is incompatible with that of the DAMA modulation at 5.2 sigmas. Aside from this annual variation, the muon data also contains a further significant modulation with a period between 10 and 11 years and a power well above the 99.9% C.L threshold for noise, whose phase corresponds well with the solar cycle: a surprising observation for such high energy muons. We see no corresponding long-period oscillation in the stratospheric temperature data.